1. Field of the Invention
The present invention relates to a sheet post-processing apparatus mounted in an image forming apparatus such as a copying machine, and more particularly, to a sheet post-processing apparatus operable to improve sheet stacking capability of sheets discharged to and stacked on a tray for stacking sheets thereon.
2. Description of the Related Art
In an image forming apparatus such as a copying machine, a sheet post-processing apparatus may be used to perform a post process such as a sorting process or a stapling process to sheets having an image formed thereon. Such a sheet post-processing apparatus stacks the sheets conveyed from the image forming apparatus on a process tray and discharges the sheets having been subjected to the stapling process to a storage tray.
However, when the sheets are not stacked in an aligned state before the sheet post-processing apparatus performs the stapling process, a problem arises in that quality of the stapling process deteriorates.
For this reason, JP-A-2001-322766 discloses a sheet alignment mechanism has been proposed in which a stack paddle is elastically deformed to align the sheets.
However, since a paddle stopper for regulating the elastic deformation of the stack paddle is away from the top surface of the sheets, a problem arises in that the sheets cannot be stably stacked and the sheet end surfaces cannot be aligned in the same direction.
Additionally, when the sheet post-processing apparatus discharges the sheets stacked in a process tray to a storage tray, a problem arises in that quality of the sorting process deteriorates because the sheets are not stacked in an aligned state.
For this reason, JP-A-7-228412 discloses a sheet post-processing apparatus including a belt that is mounted with a hook for extruding the sheets in a direction where the sheets are discharged to the process tray, and a paper discharge roller that has a clutch of a reverse rotation direction, the paper discharge roller being disposed at a position away from a belt pulley mounted with the hook in a downstream side of the process tray in a sheet conveying direction and the paper discharge roller being driven independently. At this time, a tangential speed of the paper discharge roller is set to be faster than a movement speed of the belt mounted with the hook.
However, in such a sheet post-processing apparatus, the belt mounted with the hook is away from the paper discharge roller to be independently driven. That is, a pulley of the belt mounted with the hook does not have the same rotation shaft as the paper discharge roller. As a result, a problem arises in that it is not possible to save a space because the sheet post-processing apparatus cannot be manufactured in a small size.
In addition, U.S. Pat. No. 6,786,483 B2 discloses a sheet processing apparatus in which a discharge belt provided with two bundle discharge levers is driven by a single motor to discharge a bundle of stapled sheets to a stack tray.
However, when discharging the sheets that can be easily bended, the rear end of the sheet is curved so that the bundle discharge levers pinch the rear end of the sheet. As a result, a problem arises in that a sheet conveying error or a sheet discharging error may occur.